Priority Korean Patent Application Nos. 2000-49832 filed Aug. 26, 2000 and 2001-2574 filed Jan. 17, 2001, are incorporated herein in their entirety by reference.
The present invention relates to a novel group IV metal precursor and to a chemical vapor deposition method using the precursor. More particularly, the present invention relates to a chemical vapor deposition method which comprises forming a metal oxide thin film on a substrate using a group IV metal precursor which contains a tridentate N-alkoxy-xcex2-ketoiminate ligand having a charge of xe2x88x922.
With development in the telecommunication industry, there is an increased need for the development of new electronic materials. Also, as electronic devices are continuously reduced in both size and thickness, it has become important to advance metal oxide processing technologies and, in particular, thin film formation technologies.
A Metal-Organic Chemical Vapor Deposition (MOCVD) method using volatile organometallic compounds as precursors is widely used in the deposition of metal oxide thin films, which are applied as high dielectric thin films, super-conductive thin films, electrodes, and the like. Depending on the vaporization of precursor materials, the MOCVD method is generally classified into a bubbler method and a vaporizer method. In the bubbler method, solid or liquid precursor materials are bubbled with a delivery gas to be sublimed. In the vaporizer method, precursor materials dissolved in suitable solvents are dropped onto a hot plate heated to a high temperature, so that the precursors are vaporized together with the solvents, thereby inducing efficient vaporization of the precursors. Since the vaporizer method adopts the delivery of the precursors in liquid phase, it is also known as the liquid delivery method.
In order to form thin films on substrates by chemical vapor deposition, it is first necessary to provide precursors having excellent properties. Also, good surface morphology, metal content and step coverage of the thin films formed using the precursors are necessary for their potential application as devices.
Properties of the precursors necessary for use in chemical vapor deposition include high volatility, distinct difference between vaporization temperature and decomposition temperature, low toxicity, chemical stability, thermal stability, easiness of synthesis and thermal decomposition. In addition, during the vaporization or delivery of the precursors, they must not be spontaneously decomposed or subjected to a side reaction with other precursors.
Particularly, for the formation of multi-component thin films having a high quality, metal components deposited from metal precursors on a substrate must be easily controlled in their composition, and also the metal precursors must show similar behaviors in their decomposition at the deposition temperature.
Up to now, a variety of organometallic compounds, such as metal alkyls, metal alkoxides, metal carboxylates, and metal beta-diketonates have been reported as precursors. However, these compounds did not sufficiently meet the property requirements, such as volatility, chemical and thermal stabilities, and toxicity, etc.
There were recently reported precursors of the formula M(OR)n and precursors of the formula M(OR)x(xcex2-diketonate)y in which the metal alkoxide is partially substituted with a bidentate ligand, such as xcex2-diketonate. However, such precursors still have problems in that they are susceptible to moisture due to the alkoxide ligand present in the metal complex.
When intermolecular repulsive force of precursors is increased with fluorinated alkyls substituted with fluorine atoms of high electronegativity for hydrogen atoms, volatility of the precursors is generally increased. To improve volatility of metal ions having a small charge-to-radius ratio, such as barium, strontium and the like, there are commonly used methods that introduce a bulky alkyl group-containing ligand or a polydentate Lewis base to saturate unsaturated coordination sites of the metal ions. This saturation inhibits the oligomerization and hydration of the complexes, and reduces the intermolecular interaction. However, such methods result in new problems in that grown thin films may contain fluorine, and that the Lewis base is dissociated during vaporization or delivery of the precursors.
U.S. Pat. No. 4,950,790 assigned to Air Products and Chemicals, Inc. discloses metal xcex2-ketoiminate compounds of the formula Mn+ (xcex2-ketoiminate)n which have been improved in thermal and chemical stabilities by filling vacant coordination sites of the metal with xcex2-ketoiminate as a bidentate ligand as a result of the chelate effect thereof. However, such compounds are problematic in that they are low in hydrolytic stability.
There were also reported precursors with a tridentate N-alkoxy-xcex2-ketoiminate ligand having a charge of xe2x88x922, such as Ta(N-alkoxy-xcex2-ketoiminate)(OEt3) and Nb(N-alkoxy-xcex2-ketoiminate) (OEt3). However, since these precursors contain a highly reactive alkoxide group in addition to the N-alkoxy-xcex2-ketoiminate group as a ligand, they do not contain advantages over the case where only N-alkoxy-xcex2-ketoiminate is used as a ligand.
Furthermore, in depositing a multi-component metal oxide thin film such as barium strontium titanate (BST) thin film by the MOCVD method, there have been used titanium precursors in an excess amount over barium and strontium ones due to the large difference in volatility between the metal precursors, thereby controlling the metal composition of the thin film. However, titanium used in an excess amount causes a rough surface of the thin film by forming titanium-based protrusions on the surface of the thin film (see, Japanese Journal of Applied Physics, 36, 6946 (1997)). Additionally, to apply the BST thin film to semiconductor devices such as DRAMS, the thin film must contain little or no impurities such as carbon. Also, to form a device structure, the thin film must be excellent in step coverage. However, multi-component metal oxide thin films deposited from the prior precursors are disadvantageous in that they are rough in their surface due to the use of an excess amount of the titanium precursor, they are high in their leakage current due to the presence of impurities such as carbon, etc., and they are inferior in their step coverage.
A feature of the present invention is a group IV metal precursor which exhibits excellent volatility, thermal stability and Chemical stability, and which is particularly suitable for use in the formation of multi-component metal oxide thin films containing a group IV metal such as titanium.
Another feature of the present invention is a chemical vapor deposition method using the group IV metal precursor.
In accordance with one aspect of the present invention, there is provided a tridentate ligand (L) having a charge of xe2x88x922, which is represented by the following formula (I): 
wherein each of R1 and R2, independently, is a linear or branched C1-8 alkyl group; and R3 is a linear or branched C1-8 alkylene group.
In accordance with another aspect of the present invention, there is provided an organometallic precursor of the formula M(L)2, for use in the formation of metal oxide thin films, in which M is a group IV metal ion having a charge of +4 and L is a tridentate ligand of the above formula (I) having a charge of xe2x88x922.
In accordance with still another aspect of the present invention, there is provided a chemical vapor deposition method which comprises forming a metal oxide thin film using, as a group IV metal precursor, the organometallic precursor of the formula M(L)2.